Field of the Invention
The invention relates to a semiconductor device and particularly relates to a high voltage junction field effect transistor (JFET).
Description of Related Art
High voltage devices are extensively used in power management integrated circuits (PMIC), switch mode power supplies (SMPS), and LED drivers. In recent years, green energy technology, which requires higher conversion efficiency and lower standby power consumption, is drawing more and more attention. Generally, a start-up circuit and a pulse width modulation (PWM) circuit are integrated in a switch mode power integrated circuit. The start-up circuit can be used for starting up the pulse width modulation circuit and is turned off when the pulse width modulation circuit is started up and begins to operate. Thus, the start-up circuit needs to have the characteristic of low leakage current.
Compared to the conventional power resistor or high voltage depletion NMOS (HVDNMOS), a high voltage junction field effect transistor (HVJFET) is used as the start-up circuit, which has the characteristics of high pinch off voltage and low leakage current. However, the traditional HVJFET requires a well region so as to pinch off voltage and the well is more sensitive to the process variation. As a result, the pinch off voltage may shift easily.